Node {

    String key;
   
    String value;

    List<Node> nodes;

}

Registry {

  List<Node> nodes;

}

<hibernate-mapping>

  <class name="Node" table="node">

    <id name="id" column="ID">
      <generator class="native"/>
    </id>

    <many-to-one name="parent" class="Node" column="PARENT_ID"/>

    <property name="key" column="F_KEY" not-null="true"/>

    <property name="value" column="F_VALUE" not-null="true"/>

    <set name="children" inverse="true" cascade="all">
      <key column="PARENT_ID" not-null="true"/>
      <one-to-many class="Node"/>
    </set>

</class>

</hibernate-mapping>